Conventional pulmonary rehabilitation (PR) programs are highly effective and the standard of care in patients with chronic obstructive pulmonary disease (COPD). PR faces two significant problems: (1) most patients with COPD who would benefit from PR cannot access it, and 2) there is no effective long-term strategy to maintain physical activity (PA) and benefits after completing PR. We propose a randomized controlled trial (RCT) to test the efficacy of a technology-mediated intervention to increase PA in persons with COPD who cannot access conventional, hospital-based PR. We also propose a non-randomized study to explore the ability of the PA intervention to maintain PA and exercise adherence, extending the benefits of PR, in persons with COPD who complete a conventional PR program. COPD is the third leading cause of death in the United States; an estimated 16 million Americans have COPD. Despite maximal medical therapy, patients with COPD characteristically experience breathlessness, which leads to a downward spiral of sedentary behavior, physical inactivity, deconditioning, and functional disability. Low physical activity is associated with poor outcomes in COPD--increased risk of acute exacerbations, hospitalizations, and death, independent of lung function. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recommend regular PA for all patients with COPD. Conventional, supervised PR programs clearly reduce breathlessness, and improve health-related quality of life (HRQL) and exercise capacity. However, PR programs face significant challenges of access and adherence. We developed Every Step Counts (ESC), a technology-mediated intervention based on the Behavioral Theory of Self-Regulation, to target sedentary behavior, promote PA, and alleviate deconditioning. ESC couples a website with a pedometer to directly monitor step counts. The website provides individualized step-count goals, iterative feedback, education on disease self-management, motivation, and an online community of social support. In two randomized studies in Veterans with COPD, we demonstrated ESC's safety, feasibility, and efficacy to increase PA. Accessible via the internet and available at any time from home, ESC could be an ideal low-cost platform to address the limitations of conventional PR. We hypothesize that ESC may be an efficacious strategy to promote PA in the many patients who cannot attend a PR program, and may be an option to maintain engagement in PA after patients complete a conventional PR program. Primary Aim 1: Determine the efficacy of a web-based intervention, ESC, to increase PA (measured directly with an accelerometer and a questionnaire that assesses intensity), compared to usual care, in persons with COPD who are referred to conventional PR but who cannot access it. Secondary Aim 2: Estimate the effect of the ESC intervention on (a) exercise adherence, (b) exercise self- efficacy, (c) HRQL, (d) dyspnea, (e) anxiety and depression, (f) exercise capacity, and (g) risk of acute exacerbations and COPD-related hospitalizations, compared to usual care. Exploratory Aim 3: Assess the ability of ESC to maintain PA and exercise adherence, and extend the benefits of PR, in participants with COPD who have completed conventional PR.